1. Field of the Invention
The present invention relates to memory media and input/output device packages, wireless applications and the telecommunication industry. The invention more particularly concerns a shield for the shielding of contents of a package from the effects of radio frequency and electromagnetic interference or radiation. Typically the shield holds a printed circuit board within the package, where the package conforms to the standards set by PCMCIA, JEIDA, ISO, CFA, CF Plus, miniature card, small PMCIA card, and etc. for peripheral devices.
2. Discussion of the Background
The current trend in the computing hardware, telecommunications and electronics industries is to miniaturize components and devices and to place as many of the components and devices next to each other so as to provide quality technical performance in a small package. Hardware that conveys electricity, such as a wire or printed circuit board (PCB), radiates electromagnetic radiation. The hardware is also susceptible to electromagnetic radiation radiated from other sources. The electromagnetic radiation effects the hardware by corrupting or altering the electrical signal that the component conveys. Such corruption of an electrical signal in a component is not tolerable. The power and associated affect of the electromagnetic radiation field diminishes with distance from the source of the electromagnetic radiation. Therefore, the closely placed electronic components and devices disadvantageously influence each other by radiating electromagnetic fields. Placement of electronic components and devices in close proximity to each other would be acceptable if the effects of the electromagnetic radiation emanating from each device could be muted or lessened to a degree where the electromagnetic radiation emanating from each device does not corrupt the electrical signals being conveyed by other components or devices.
Furthermore, shielding is especially important in high speed data transfer situations, such as in fiber optic applications.
Furthermore, another need of the industry is to produce rugged PMCIA-style cards, and I/O device cards or packages which are capable of being handled by end-users in a rough manner or environment. End-users, in use, tend to impart bending and torsional loads on the packages. After being subjected to such loads, the contents of the packages do not operate properly.
Prior art PMCIA cards typically have two sheet metal covers which are joined together by a plastic frame molded around each cover, as disclosed in U.S. Pat. No. 5,397,857. U.S. Pat. No. 5,397,857 is hereby incorporated by reference. The electrically conductive, sheet metal of the top and bottom covers provide a shielding effect against the transmission of electromagnetic radiation through the top and bottom covers. Other cards have plastic covers which result in electromagnetic radiation being transmitted through the covers. A seam is formed where the top cover and the bottom cover meet. Electromagnetic radiation is able to pass through the region of the seam since the seam is substantially constructed of plastic material which is, in its natural state, electrically non-conductive, where the plastic material does not provide a shielding effect against electromagnetic radiation, whether the electromagnetic radiation is radiated from components within the PCMCIA card or whether the radiation is radiated from other components external to the PCMCIA card and passes through the seam and into the interior of the PCMCIA card. The PCMCIA card can be completely constructed of plastic material and the two halves of the package can be sonically bonded or laser welded. Such leakage issues are also present in compact flash packages, miniature cards, and other PC card packages, where the term PC card package is inclusive of any package which can contain electrical components, such as the devices described above, and is not to be limited by any narrow definition of the term as used in trade groups.
Other prior art packages employ a clip, veneer, or rail of conductive material positioned around the side edges of the package so as to shield against electromagnetic radiation, as disclosed in U.S. Pat. No. 5,333,100. This approach causes the overall dimensions of the resulting package to exceed the standards set by industry. Another prior art solution, such as U.S. Pat. Nos. 5,505,628 and 5,476,387, employ the use of covers that have mechanical overlaps which attach one cover to the other cover at discrete intervals along the side edge of the package. The mechanical overlaps electrically ground the two covers to each other. The mechanical overlaps traverse or cross over the side edge of the package, as such, only intermittent shielding is provided, which is not acceptable. Such solutions, however, adds to the size, complexity, material cost, and labor cost of the package.
Another prior art shield, as disclosed in U.S. Pat. No. 5,005,106, consists of a sheet-like material that has the appearance of an envelope, where the shield slips over the printed circuit board. The shield protects the printed circuit board from electromagnetic radiation. The shield is designed to be used with packages that have covers constructed of a plastic material. As such, the printed circuit board needs to be insulated from electromagnetic radiation traversing the plastic covers and frames. Furthermore, the sheet-like material of the shield does not provide structural support to the covers and frames of the package.
Thus, there is a need for a simple to manufacture and assemble package that shields the seam of the device package from electromagnetic radiation, while, at the same time, provides a package which is structurally rugged.